The wide variety of substances, such as chemicals, oil, gas or coolants as well as steam for transmitting energy, are transported and distributed in pipeline systems of the process engineering industry. Since these media have very different physical properties, measuring devices which are based on different measurement principles, for example also the vortex principle, exist for the purpose of determining flow rate values and other parameters. Vortex flowmeters belong to the standard measuring devices for determining the volumetric flow rate of liquids, gases and vapors. In this case, vortex flowmeters can also be used in non-conductive measurement media and thus supplement the magnetoinductive flowmeters which are likewise known.
The measurement principle of vortex flowmeters is based on the Kármán vortex street, in which case opposed vortices occur downstream of a body around which the flow passes. This phenomenon is used when measuring the vortex flow rate by introducing, into a measuring tube, a disruptive body downstream of which said vortex street forms. Since the individual vortices run in opposite directions and with an offset with respect to one another, local pressure differences form and can be detected using a downstream sensor. The so-called vortex frequency is determined using the sensor by counting the pressure pulses occurring per unit time. The greater the flow velocity, the higher the measured vortex frequency as well. In practice, the flow velocity of the measurement medium needed to form the vortex is often too low. However, installing a vortex counter in a measuring tube with a reduced tube cross section makes it possible to accordingly increase the flow velocity of the measurement medium, to be precise without restricting the measurement accuracy. The temperature sensor optionally installed in the sensor provides additional possible uses. In this manner, it is also possible to calculate temperature-dependent masses and thermal flows, which is specified, in particular, in auxiliary industrial circuits with saturated steam or gas.
In known systems, different types of sensors are used for detecting the vortex frequency, such as the frequency of the vortex separations downstream of the vortex body. Capacitive sensors, thermistors, diaphragms, strain gauges, fiber optic sensors and ultrasonic sensors or piezoelectric elements are used, inter alia, for this purpose.
WO 98/43051 A1 discloses a vortex flowmeter of the generic type in which a sensor for detecting the vortex frequency is arranged in a measuring tube. An electronic evaluation unit which is connected downstream of the sensor and has a filter circuit that receives the measurement signal from the sensor and calculates an output value which indicates the fluid flow rate. An additional temperature sensor detects the temperature of the measurement medium and generates a supplementary measured temperature value, while a likewise additional pressure sensor provides the electronic evaluation unit with the pressure of the measurement medium for the purpose of signal processing. The electronic evaluation unit calculates a calibration factor as a function of the output signal, the temperature value and the pressure value for use in calculating the output value which indicates the flow rate of the measurement medium.
Integrating the additional sensors for determining the pressure and, in particular, the temperature in the sensor system coming into contact with the measurement medium specifies a large outlay on components. The individual sensors also need to be wired to one another, which increases the installation complexity.
Exemplary embodiments of the present disclosure provide a vortex flowmeter having a sensor for detecting the vortex frequency, the temperature-measuring means of which have a simple design and can be inserted into the sensor system with little effort.
Exemplary embodiments of the present disclosure provide that the sensor for detecting the vortex frequency includes (e.g., consists of) a carrier body on which a plurality of piezoelectric elements, which are arranged at a distance from one another and are intended to measure the frequency, and a temperature-measuring element are placed.
An advantageous result of the exemplary embodiments disclosed herein provides, that the means for measuring the temperature are not in the form of an independent sensor component but rather are part of the sensor for detecting the vortex frequency and form a functional unit with the carrier body of said sensor.
Instead of the piezoelectric elements, it is also possible to use other suitable measuring sensors within the scope of the disclosed exemplary embodiments provided that said sensors can be applied to the carrier body in the manner according to the respective exemplary embodiments.
The carrier body can include (e.g., consists of) a ceramic material, at least the piezoelectric elements being fixed to the carrier body in a manner embedded in ceramic cement. As a result, the piezoelectric elements can be reliably connected to the ceramic carrier body in such a manner that the vibrations of the carrier body are reliably forwarded to the piezoelectric elements for measurement.
In an exemplary embodiment, the carrier body is formed from two carrier body halves, which are adhesively bonded to one another and enclose the piezoelectric elements and the temperature-measuring element. Two cuboidal basic bodies which have an elongated shape and are intended to have recesses for accommodating the piezoelectric elements and the temperature-measuring element in the side surfaces which come into contact with one another are suitable as carrier body halves.
The plurality of contacts which are needed to connect the piezoelectric elements and the temperature-measuring element should be arranged together on the end side at the proximal end of the carrier body. The electrical signal cables which continue on can be reliably fitted at this position without impeding the vibrational properties of the carrier body or coming into contact with the measurement medium. Each piezoelectric element and the temperature-measuring element should be connected via an associated pair of electrical contacts.
In order to additionally protect the electrical connection of the signal cables to the electrical contacts, it is proposed that this contact-making region is provided with a glass cover in a fixed position in order to fix the signal cables in their position relative to the sensor. The signal cables can be connected to the electrical contacts of the sensor with an integral material joint by means of welding and are covered with the glass cover.
According to another exemplary embodiment, a total of three piezoelectric elements are arranged at a distance from one another between the electrical contacts at the proximal end of the carrier body, on the one hand, and the temperature-measuring element at the distal end of the carrier body, on the other hand. As a result, the individual sensor components can be functionally accommodated along the elongated carrier body. Since the temperature-measuring element is positioned at the distal end of the carrier body, it projects into the flowing measurement medium to the maximum extent in order to reliably measure the temperature.
An electrical resistance thermometer, especially a PT100 sensor which, available as a standardized component, can be integrated on the carrier body in a space-saving manner, is suitable, in particular, as the temperature-measuring element.
According to another exemplary embodiment for producing the sensor system of the carrier body, the temperature-measuring element, the electrical conductor tracks connecting the latter and the piezoelectric elements, including the electrical contacts on the end side, and also the contact areas for the piezoelectric elements to be used are produced by vapor-depositing a precious metal on the ceramic carrier body. Platinum which produces the abovementioned components after vapor deposition and subsequent laser treatment is suitable, in particular, for this purpose. This can be implemented in a simple manner in terms of process engineering in series production.
The contact areas produced in the above way for the piezoelectric elements can be connected to the latter by a conductive adhesive producing an area contact and a wrap-around contact. A polyimide conductive adhesive can be used as the electrical conductive adhesive.
In order to electrically insulate the individual components, another exemplary embodiment includes a measure in which at least the temperature-measuring element and the conductor tracks are provided with a glass layer applied thereto. This glass layer is supplemented, in the region of the outer electrical contacts, with the abovementioned glass cover in the contact-making region, thus producing continuous insulation.
In order to additionally seal against moisture, the outside of the entire sensor can be coated with a plastic layer which likewise can include (e.g., consists of) a polyimide film. The carrier body of the sensor may be additionally cemented in a metal sleeve so that the flowing measurement medium cannot damage the carrier body of the sensor as a result of direct contact.